RF pulse generation for magnetic resonance imaging

Abstract

An imaging system includes determination of a first range of values of an imaging parameter, determination of a cost function expressing a difference between a first pulse profile and a second pulse profile, the second pulse profile generated based on respective values of each of a set of pulse parameters, identification of first coefficient values of each function of a set of functions which substantially minimize the cost function over the first range of values of the imaging parameter, where each of the set of functions determines a value of a respective one of the set of pulse parameters based on a value of the imaging parameter, and storage of the first coefficient values of each function of the set of functions in association with the first range of values.

What is claimed is: 
     
       1. A system comprising:
 a chassis defining a bore; 
 a main magnet to generate a polarizing magnetic field within the bore; 
 a gradient system to apply a gradient magnetic field to the polarizing magnetic field; 
 a radio frequency system to apply an excitation pulse to a patient tissue disposed within the bore and to receive signals from the patient tissue; 
 a sequence controller to control generation of the excitation pulse by the radio frequency system; and 
 a computing system to receive the signals from the radio frequency system, the computing system to execute program code to:
 determine a first range of values of an imaging parameter; 
 determine a cost function expressing a difference between a first pulse profile and a second pulse profile, the second pulse profile generated based on respective values of each of a set of pulse parameters; 
 identify first coefficient values of each function of a set of functions which substantially minimize the cost function over the first range of values of the imaging parameter, where each of the set of functions determines a value of a respective one of the set of pulse parameters based on a value of the imaging parameter; 
 store the first coefficient values of each function of the set of functions in association with the first range of values; 
 determine the value of the imaging parameter; 
 
 determine, for each function of the set of functions, a value of a pulse parameter based on the first coefficient values of the function and the value of the imaging parameter; and 
 control the radio frequency system to generate a pulse based on the pulse parameter values. 
 
     
     
       2. A system according to  claim 1 , wherein the imaging parameter is slice thickness. 
     
     
       3. A system according to  claim 1 , the computing system to further execute program code to:
 determine a second range of values of the imaging parameter; 
 identify second coefficient values of each function of the set of functions which substantially minimize the cost function over the second range of values of the imaging parameter; and 
 store the second coefficient values of each function of the set of functions in association with the second range of values. 
 
     
     
       4. A system according to  claim 1 , the computing system to further execute program code to:
 determine a type of radio frequency pulse; and 
 determine the set of functions based on the type of radio frequency pulse. 
 
     
     
       5. A system according to  claim 1 , wherein the radio frequency system is responsive to a scan prescription and a direction from the sequence controller to produce the excitation pulse having a predetermined frequency, a predetermined phase, and a predetermined pulse amplitude waveform. 
     
     
       6. A system according to  claim 1 , further comprising:
 a plurality of amplifiers, wherein each amplifier includes a digital-analog converter, and the digital-analog converter of each amplifier is controlled by the sequence controller to generate a gradient pulse. 
 
     
     
       7. A computer-implemented method comprising:
 determining a first range of values of an imaging parameter for a MRI system; 
 determining a cost function expressing a difference between a first pulse profile and a second pulse profile, the second pulse profile generated based on respective values of each of a set of pulse parameters; 
 identifying first coefficient values of each function of a set of functions which substantially minimize the cost function over the first range of values of the imaging parameter, where each of the set of functions determines a value of a respective one of the set of pulse parameters based on a value of the imaging parameter; 
 storing the first coefficient values of each function of the set of functions in association with the first range of values in a memory; 
 determining a second range of values of the imaging parameter; 
 identifying second coefficient values of each function of the set of functions which substantially minimize the cost function over the second range of values of the imaging parameter; 
 storing the second coefficient values of each function of the set of functions in association with the second range of values; 
 determining the value of the imaging parameter; 
 determining whether the value of the imaging parameter is within the first range of values or within the second range of values; 
 if the value of the imaging parameter is within the first range of values, determining, for each function of the set of functions, a value of a pulse parameter based on the first coefficient values of the function and the value of the imaging parameter; 
 if the value of the imaging parameter is within the second range of values, determining, for each function of the set of functions, a value of a pulse parameter based on the second coefficient values of the function and the value of the imaging parameter; and 
 controlling a radio frequency system to generate a pulse based on the pulse parameter values, wherein the MRI system further comprises: 
 a chassis defining a bore; 
 a main magnet to generate a polarizing magnetic field within the bore; 
 a gradient system to apply a gradient magnetic field to the polarizing magnetic field; 
 a radio frequency system to apply an excitation pulse to a patient tissue disposed within the bore and to receive signals from the patient tissue; and 
 a sequence controller to control generation of the excitation pulse by the radio frequency system. 
 
     
     
       8. A method according to  claim 7 , wherein the imaging parameter is slice thickness. 
     
     
       9. A method according to  claim 7 , further comprising:
 determining a type of radio frequency pulse; and 
 determining the set of functions based on the type of radio frequency pulse. 
 
     
     
       10. A method according to  claim 7 , wherein the radio frequency system is responsive to a scan prescription and a direction from the sequence controller to produce the excitation pulse having a predetermined frequency, a predetermined phase, and a predetermined pulse amplitude waveform. 
     
     
       11. A method according to  claim 7 , further comprising:
 a plurality of amplifiers, wherein each amplifier includes a digital-analog converter, and the digital-analog converter of each amplifier is controlled by the sequence controller to generate a gradient pulse. 
 
     
     
       12. A non-transitory computer-readable medium storing program code, the program code executable by a computer system to cause the computer system to:
 determine a first range of values of an imaging parameter for a MRI system; 
 determine a cost function expressing a difference between a first pulse profile and a second pulse profile, the second pulse profile generated based on respective values of each of a set of pulse parameters; 
 identify first coefficient values of each function of a set of functions which substantially minimize the cost function over the first range of values of the imaging parameter, where each of the set of functions determines a value of a respective one of the set of pulse parameters based on a value of the imaging parameter; 
 store the first coefficient values of each function of the set of functions in association with the first range of values in a memory; 
 determine the value of the imaging parameter; 
 determine, for each function of the set of functions, a value of a pulse parameter based on the first coefficient values of the function and the value of the imaging parameter; and 
 control a radio frequency system to generate a pulse based on the pulse parameter values, wherein the MRI system further comprises: 
 a chassis defining a bore; 
 a main magnet to generate a polarizing magnetic field within the bore; 
 a gradient system to apply a gradient magnetic field to the polarizing magnetic field; 
 a radio frequency system to apply an excitation pulse to a patient tissue disposed within the bore and to receive signals from the patient tissue; and 
 a sequence controller to control generation of the excitation pulse by the radio frequency system. 
 
     
     
       13. A medium according to  claim 12 , wherein the imaging parameter is slice thickness. 
     
     
       14. A medium according to  claim 12 , the program code further executable by a computer system to cause the computer system to:
 determine a second range of values of the imaging parameter; 
 identify second coefficient values of each function of the set of functions which substantially minimize the cost function over the second range of values of the imaging parameter; and 
 store the second coefficient values of each function of the set of functions in association with the second range of values. 
 
     
     
       15. A medium according to  claim 12 , the program code further executable by a computer system to cause the computer system to:
 determine a type of radio frequency pulse; and 
 determine the set of functions based on the type of radio frequency pulse. 
 
     
     
       16. A medium according to  claim 12 , wherein the radio frequency system is responsive to a scan prescription and a direction from the sequence controller to produce the excitation pulse having a predetermined frequency, a predetermined phase, and a predetermined pulse amplitude waveform. 
     
     
       17. A medium according to  claim 12 , further comprising:
 a plurality of amplifiers, wherein each amplifier includes a digital-analog converter, and the digital-analog converter of each amplifier is controlled by the sequence controller to generate a gradient pulse.